Smithfield climate

Smithfield Frost Dates and Growing Season

NOAA 1991-2020 normals for Grays Landing, 9.5 km from Smithfield, elevation 800 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Grays Landing. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around April 28 and the first fall freeze around October 21, a growing season of about 175 days.

Median at 36°F
last May 8, first October 11
Median at 32°F
last April 28, first October 21
Median at 28°F
last April 16, first October 31

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold10%20%30%40%50%60%70%80%90%
36°FMay 23May 18May 14May 11May 8May 6May 2Apr 30Apr 25
32°FMay 14May 8May 4Apr 30Apr 28Apr 24Apr 22Apr 19Apr 15
28°FMay 1Apr 25Apr 21Apr 18Apr 16Apr 13Apr 9Apr 6Apr 1
24°FApr 17Apr 12Apr 8Apr 6Apr 3Apr 1Mar 29Mar 24Mar 19
20°FApr 6Apr 1Mar 30Mar 26Mar 23Mar 20Mar 16Mar 11Mar 6
16°FMar 29Mar 24Mar 19Mar 15Mar 11Mar 8Mar 4Feb 28Feb 20

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold10%20%30%40%50%60%70%80%90%
36°FSep 29Oct 3Oct 6Oct 9Oct 11Oct 13Oct 16Oct 19Oct 24
32°FOct 9Oct 13Oct 16Oct 18Oct 21Oct 23Oct 26Oct 29Nov 1
28°FOct 19Oct 23Oct 26Oct 29Oct 31Nov 2Nov 5Nov 8Nov 12
24°FOct 30Nov 1Nov 4Nov 7Nov 10Nov 12Nov 14Nov 19Nov 24
20°FNov 5Nov 10Nov 14Nov 17Nov 21Nov 24Nov 29Dec 2Dec 8
16°FNov 13Nov 19Nov 25Nov 29Dec 3Dec 7Dec 14Dec 20Dec 26

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold10%20%30%40%50%60%70%80%90%
36°F175168164159155151147142135
32°F193187183179175171168163156
28°F217210206202198194190185176
24°F242235230225222218214209204
20°F269260254248244239235229221
16°F297287281275269264258251241

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
100% of years
32°F or colder
100% of years
28°F or colder
100% of years
24°F or colder
100% of years
20°F or colder
100% of years
16°F or colder
100% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F
5,578
Cooling degree days, base 65°F
756
Growing degree days, base 40°F
5,394
Growing degree days, base 45°F
4,175
Growing degree days, base 50°F
3,105
Growing degree days, base 55°F
2,180
Growing degree days, base 60°F
1,393

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,09703
February93005
March792028
April4375123
May18244339
June32140558
July3256718
August5216676
September7785459
October37011166
November689025
December96405

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 9.5 km from Smithfield. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00363451 (Grays Landing). Public domain.